1. Field
The present invention relates to a magnetic detection device for detecting an external magnetic field by using a magneto-resistance element, and more particularly, to a magnetic detection device for detecting a magnetic field with high precision by adjusting a resistance, and also relates to a method of manufacturing the magnetic detection device.
2. Description of the Related Art
Generally, when a variable resistance layer of which the resistance varies with an external environment is used to detect a variation of the external environment, the variable resistance layer is connected in series to a reference resistance layer of which the resistance does not vary, and a voltage is applied to the variable resistance layer and the reference resistance layer connected in series to each other. A central potential between the variable resistance layer and the reference resistance layer is detected so as to detect a variation of the resistance of the variable resistance layer without being greatly influenced by environmental temperature.
In such type of detection device, it is necessary to adjust the resistance of the reference resistance layer so as to adjust the central potential between the variable resistance layer and the reference resistance layer, and it is preferable to adjust the resistance of the reference resistance layer so as to set the central potential equal to a one-half of a supply voltage.
In general, in order to adjust the resistance of the reference resistance layer, after forming the reference resistance layer, the reference resistance layer is trimmed so that the resistance thereof is set to a desired resistance.
JP-2001-167902 is an example of the related art.
However, when the resistance of the reference resistance layer is adjusted through the trimming process, the adjustment process thereof is complicated. When the reference resistance layer is formed of a single material layer, the reference resistance layer should not be damaged by the trimming process.
However, when the resistance layer of which the resistance is to be adjusted is a magneto-resistance layer having a multi-layer structure, or the reference resistance layer of which the resistance is to be adjusted so that the resistance is equal to that of the magneto-resistance layer also has the multi-layer structure as in the case of the magneto-resistance layer, too much stress is applied between each of the layers in the multi-layer structure at the time of trimming the resistance layer. Accordingly, the structure of the resistance layer may be partially destroyed, thereby changing a temperature characteristic and thus deteriorating a magneto-resistance effect.